The objective of this research is the identification of biochemical and genetic mechanisms which regulate the rate of human purine nucleotide synthesis and coordinate the activity of this pathway with that of other biosynthetic pathways. Previous investigations have established a number of discrete enzyme abnormalities which express themselves clinically in gout with excessive purine production. While studies of these genetic alterations have contributed to contemporary concepts of the biochemical control of purine nucleotide synthesis, particularly emphasizing the importance of the intracellular concentrations of 5-phosphoribosyl l-pyrophosphate (PRPP) and inhibitory purine nucleotides, the basis of disordered purine metabolism in the majority of individuals with gout remains unknown. In the proposed clinical studies, the extent to which kinetic variation within known enzyme abnormalities accounts for this deficit in our understanding will be evaluated and an attempt to identify and characterize additional enzyme abnormalities among patients with gout and purine overproduction will be made. The delineation of additional regulatory determinants will also be the aim of studies of (1) the effects of chemical and pharmacological agents on human purine metabolism in vivo and (2) the importance of the intracellular concentration of ribose-5-phosphate in determining PRPP generation in human fibroblasts in culture. On the supposition that coordination of biosynthetic pathways requires some common control mechanism, the role of PRPP, an important regulatory compound in purine synthesis, in determining the rate of synthesis of pyrimidine nucleotides will be evaluated in human lymphoblasts in tissue culture. The synthesis of PRPP is catalyzed by the enzyme PRPP synthetase. A dominantly inherited increase in activity of this enzyme has recently been shown to be a cause of purine overproduction and gout providing a potential model for the study of dominantly inherited metabolic disorders. Detailed study of a purified mutant human PRPP synthetase in which a structural alteration results in an increased enzyme specific activity per molecule will be undertaken in attempt to delineate in detail the structure basis of this unusual genetic alteration in enzyme activity.